Textile coatings on belts, in particular toothed belts, are primarily designed to reduce abrasion and, in the case of toothed belts, to stop tearing at the tooth edges and tear propagation in the event of damage in the tooth outside edge.
Polyurethane belts are generally cast directly onto the textile overlay, so it is on the overlay that the polyurethane reacts, crosslinks and solidifies. In the process, it penetrates to at least some extent into the textile and therethrough. As the abrasion-resistant and optionally friction-reducing textile overlay then somewhat wears away during use, the belt polyurethane, which generally has a very high coefficient of friction, comes into direct contact with the power transmission or toothed disk, so there is an abrupt increase in the level of friction there. This is undesirable.
DE 10 2008 055 497 A1 discloses providing an adhesion promoter between the foundational body and the textile overlay of a drive belt in order to avoid excessively deep penetration of the vulcanizate into the textile overlay and to effect better chemical attachment to the textile. The adhesion promoter melts in the course of vulcanization and penetrates into the textile overlay while undergoing co-crosslinking. The process is unsuitable for polyurethane belts, since it prevents the inherently desirable mechanical intermeshing between the polyurethane and the textile and shortens the durability and/or maximum service life of the belt.
U.S. Pat. No. 6,296,588 B1 further discloses endowing the textile overlay of an endless belt with an additional layer of a high-melting thermoplastic. The additional level of abrasion control provided by this, however, only lasts until the thermoplastic on the surface has worn away in use. From that point on, friction is liable to increase very suddenly with the advent at the surface of polyurethane which, in the course of being used to cast the belt, has penetrated the through textile to the thermoplastic layer.
To rectify the increased friction, therefore, it has also already been proposed that the textile overlay be additionally rendered lubricious. This is frequently accomplished with PTFE which, however, tends to break and is too rapidly lost during use as the fibers rub against each other. Such textiles as are additionally rendered lubricious by means of PTFE are known, for example from WO 03/031700 A1 and US 2010/0120566 A1. The US 2010/0120566 A1 proposal is that the woven fabric comprising PTFE fibers should also incorporate low-melting thermoplastic fibers which melt in the event of thermal forcing and fix the PTFE fibers. Since this form of fixing surrounds the PTFE fibers, however, it simultaneously hinders the friction-ameliorating improvement.